1. Technical Field
The present invention relates to a driving machine for driving a fastening member such as a nail using compressed air as a power source.
2. Background Art
Description will be given below of an example of a conventional driving machine with reference to FIGS. 6 and 7.
FIG. 6 is a broken section view of the main portions of a conventional driving machine, and FIG. 7 is an enlarged section view of the main portions shown in FIG. 6. In the illustrated driving machine, compressed air, which is supplied from a compressor (not shown), is accumulated through an air hose (not shown) into a pressure storage chamber 2 formed in a driving machine main body 7. Within the driving machine main body 7, there is provided a tubular-shaped cylinder 5; and, into the cylinder 5, there is fitted a piston 4 which can be slid in a reciprocating manner.
On the lower portion of the piston 4, there is provided a driver 22 integrally therewith. Between a magazine (not shown) and a nose portion 23, there is interposed fastening member feed means 25. Fastening members 28 such as nails stored in the magazine are fed one by one into a shooting opening 24 formed in the nose portion 23 by the fastening member feed means 25.
Here, the fastening member feed means 25 is composed of a fastening member feed cylinder 12 and a fastening member feed piston 11. The fastening member feed piston 11 is fitted into the fastening member feed cylinder 12 in such a manner that it can be slid back and forth within the fastening member feed cylinder 12. Also, on the leading end of the fastening member feed piston 11, there is mounted a feed pawl 14 in such a manner that it can be rotated. When the fastening member feed cylinder 12 is operated, the feed pawl 14 can be moved reciprocatingly together with the feed piston 11 along a feed passage 29. When the feed pawl 14 moves backward, it comes in contact with the shaft of the fastening member 28 within the feed passage 29 and is thereby rotated in such a manner as to retreat from the feed passage 29, so that it moves beyond the fastening member 28; and, when the feed pawl 14 moves forward, it advances into the feed passage 29 and is engaged with the shaft of the fastening member 28 to thereby feed the fastening member 28.
Next, when a trigger 1 is pulled, there is started a driving process in which a cylinder valve 3 sealing the upper end of the cylinder 5 is opened, and the compressed air of the pressure storage chamber pushes down the piston 4, whereby the fastening member 28 fed into the shooting opening 24 of the nose portion 23 by the fastening member feed means 25 is driven by the leading end of the driver 22. Also, after the fastening member 28 is driven, the piston 4 collides with a bumper 8, whereby the remaining surplus energy of the piston 4 is absorbed by the bumper 8. When the piston 4 passes through air holes 5a, a portion of the compressed air is supplied through the air holes 5a and a check valve 50 to a return air chamber 6. Further, a portion of the compressed air supplied to the return air chamber 6 flows from the return air chamber 6 and is stored through air passages 18 and 19 into the fastening member feed cylinder 12, which pushes down the fastening member feed piston 11 that is tightly fitted with and is slid within the fastening member feed cylinder 12, thereby causing the feed pawl 14 to move backward.
When the trigger 1 is released, the pressure of the return air chamber 6 pushes back the piston 4 and, at the top dead center of the piston 4, the compressed air of the return air chamber 6 is exhausted from a lower exhaust port 21 existing downward of the bumper 8 or from an upper exhaust port 27 through a clearance formed upwardly of the cylinder 5; and, the feed pawl 14 is returned to its original position by a return spring 13.
Also, between a main body side passage 18 communicating with the return air chamber 6 on the main body 7 side and an air passage 19 communicating with the inside of the fastening member feed cylinder 12, there is interposed a plate-shaped filter portion 17 having a plurality of small holes 20 while the connecting portions of the passages 18 and 19 are sealed by packing 16a; and thus, an effective sectional area equal to the conventional passage area is secured by the plurality of small holes 20 (see the patent reference 1 Japan Utility Model Application No. 2510176).
In the above-mentioned conventional driving machine, when the above-mentioned driving operation is carried out repeatedly tens of thousands times, owing to the impact fatigue, there are caused cracks on the upper surface of the bumper 8 which is used to absorb the impact of the surplus energy, thereby forming a small broken piece 30 shown in FIG. 7. This small broken piece 30, in most cases, is discharged from the lower exhaust port 21. However, in some cases, the small broken piece 30 is moved from a return chamber passage hole 9 through the air passages 18 and 19 into the fastening member feed cylinder 12, and is accumulated in the periphery of the fastening member feed piston 11, which makes it impossible for the fastening member feed piston 11 to return to its normal position. As a result of this, the feeding operation of the fastening member feed piston 11 is incomplete, that is, the normal feeding of the fastening member 28 is impossible.
Therefore, according to the patent reference 1, in a structure in which, between the air passages, there is interposed a plate-shaped filter portion for preventing the entrance of the broken piece of the bumper, in order to prevent the broken pieces of the bumper from entering the fastening member feed cylinder, they are accumulated on the air passages using the compressed air; and, the broken pieces, which have entered the air passages once, are crammed into the air passages and are thus hard to be discharged into the return air chamber, with the result that the broken pieces close the air passages respectively formed between the return air chamber and feed cylinder. This raises the following problems: that is, a sufficient amount of compressed air cannot be supplied to the fastening member feed cylinder, and the compressed air supplied to the fastening member feed cylinder cannot be exhausted, whereby the forward and backward movements of the feed piston are made incomplete and, therefore, the fastening members such as connected nails cannot be fed properly.